Understanding of the pathophysiology of non-occlusive mesenteric ischemia is incomplete and the methods for diagnosis and treatment uncertain. At postmortem examination, intestinal infarction may be due to either vascular obstruction of the mesenteric circulation by thromboemboli or to a low flow state with patent mesenteric arteries. Presently, there is no way to distinguish clinically the obstructive from the non-obstructive form of mesenteric ischemia since both are likely to occur in patients with a history of cardiac disease, lowered cardiac output and arrhythmias. Furthermore, infarction of the bowel can only be diagnosed at the time of laparotomy. There are four objectives of the proposed research: (1) to develop an isotopic marker of bowel ischemia and/or infarction which will permit earlier diagnosis without necessitating laparotomy; (2) to understand more clearly the pathophysiology of non-occlusive mesenteric ischemia by quantifying the angiographic vasoconstriction which is observed radiographically and to determine the role, if any, of arteriovenous shunting in this syndrome; (3) to study a variety of vasodilators to determine which is optimal for reversing vasoconstriction of the mesenteric circulation associated with non-occlusive mesenteric ischemia of cardiac origin; and (4) to use or observations from the experimental models to formulate improved disgnostic approaches and treatment plans for patients with this syndrome.